The sensing performance of chemical sensors can be achieved not only by modification or hybridization of sensing materials but also through new design in device geometry. The performance of a chemical sensing device can be enhenced from a simple three-dimensional (3D) chemiresistor-based gas sensor platform with an increased surface area by forming networked, self-assembled reduced graphene oxide (R-GO) nanosheets on 3D SU8 micro-pillar arrays. The 3D R-GO sensor is highly responsive to low concentration of ammonia (NH3) and nitrogen dioxide (NO2) diluted in dry air at room temperature. Compared to the two-dimensional planar R-GO sensor structure, as the result of the increase in sensing area and interaction cross-section of R-GO on the same device area, the 3D R-GO gas sensors show improved sensing performance with faster response (about 2%/s exposure), higher sensitivity, and even a possibly lower limit of detection towards NH3 at room temperature.